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Caption

DNA chemistry. Computer model of part of the DNA chemistry of the E. coli bacterium (Escherichia coli). A DNA (deoxyribonucleic acid) strand (blue) is being modified by a CAP protein (orange/purple) so that a gene (DNA section) can be activated. The CAP (catabolite gene activation protein) is bound to a DNA promotor region, allowing RNA polymerase (a genetic transcriptor) to 'read' the genes that contain the instructions for making the enzymes for lactose metabolism. This use of a CAP allows the bacteria to adapt to conditions where glucose (its normal food source) is not available, and to metabolise lactose instead.